The present invention relates to a small hole electric discharge machine and more particularly to a small hole electric discharge machine for forming ultrafine holes in a workpiece by generating electric discharge between a rotating long thin pipe electrode and the workpiece, and more particularly still to a pipe electrode holder for holding the pipe electrode, which can be attached to a rotating spindle of the small hole electric discharge machine so that the pipe electrode is arranged coaxially with the rotating spindle.
When forming a start hole in a workpiece in order to pass a wire electrode through, for example, a small hole electric discharge machine is utilized that uses a copper or copper alloy pipe electrode having an external diameter of 0.30 to 0.05 mm. The pipe electrode is arranged vertically coaxial with a rotating spindle holder of the small hole electric discharge machine by a pipe electrode holder. By causing electric discharge between the pipe electrode and the workpiece, and feeding the pipe electrode downwards, an ultrafine hole is formed in the workpiece. During machining, dielectric fluid is supplied to the hole being formed in the workpiece by being passed through the pipe electrode. The inner diameter of the pipe electrode is normally 0.12 mm when the external diameter is 0.30 mm, 0.07 mm when the external diameter is 0.15 mm, and 0.04 mm when the external diameter is 0.1 mm. It is known that these types of small diameter pipe electrodes are severely consumed during machining. The length to which the pipe electrode is consumed may be the same or even greater than the extent to which the pipe electrode is moved downwards. In order to reduce the frequency of replacing the pipe electrode, the pipe electrode has a length a few hundred times larger than the outer diameter, namely 100-500 mm. A small hole electric discharge machine has a power supply for supplying current to the pipe electrode, and a fluid supply device for supplying dielectric fluid into the pipe electrode.
Japanese Patent Laid-open No. 8-290332 discloses a pipe electrode holder including a collet for gripping a pipe electrode. The collet is fitted into a through hole of a cylinder, and an upper end of the cylinder is capable of being attached to a lower end of a rotating spindle of the small hole electric discharge machine, while a lower end of the cylinder is screwed into a cap nut. An operator first inserts the pipe electrode into a through hole of the collet from the lower end of the cylinder. The force with which the collet holds the pipe electrode can be adjusted by tightening the cap nut. If the cap nut is tightened, the collet moves upward in the axial direction. In this way, a vertical joint in the collet is closed up to hold the pipe electrode tightly. During this operation, it is quite common for accidents to occur where the operator touches the pipe electrode causing it to become bent.
An object of the present invention is to provide a pipe electrode holder capable of moving a collet in an axial direction at an upper side of a cylinder to close a joint in the collet, so that an operator does not bend the pipe electrode.
Another object of the present invention is to provide a pipe electrode holder having a pipe electrode reliably arranged coaxial with a rotating spindle of a small hole electric discharge machine when the pipe electrode holder is attached to the rotating spindle.
Other objects of the present invention will become clear to a person skilled in the art upon reference to the following description and practicing the invention.
In order to achieve the above described objects, a pipe electrode holder for holding a pipe electrode, according to the present invention, is capable of being coaxially attached to a rotating spindle of a small hole electric discharge machine, and comprises a cylinder (1) capable of being fitted into a rotating spindle (7), having a threaded upper end and a through hole (1a), a collet (2), having a hole (2a) through which the pipe electrode (6) passes, fitted into the through hole of the cylinder, for gripping a pipe electrode, and a holder head (5) for screwing into the threaded upper end of the cylinder so as to make the gripping force of the collet adjustable.
Preferably, the pipe electrode holder further comprises an elastic seal block (4), having a through hole (4a) through which the pipe electrode passes, fitted into the through hole of the cylinder between the collet and the holder head.
More preferably, the pipe electrode holder further comprises a washer (3), having a through hole (3a) through which the pipe electrode passes, fitted into the through hole of the cylinder between the collet and the seal block.
The collet preferably has a first tapered surface (2d) with a joint, and the washer preferably has a tapered surface (3d) for engaging with the first tapered surface.
The collet also preferably has a second tapered surface (2c, 2e) having a joint, and a tapered surface (1c, 1h) for engaging with the second tapered surface is formed in the through hole of the cylinder.
In order to reliably arrange the pipe electrode coaxially with the rotating spindle, a flange (1f) extending radially and capable of contacting a bottom surface of the rotating spindle is preferably formed in the cylinder.
A flange (5d) extending radially and capable of contacting a top face of the cylinder is preferably formed on the holder head.